This invention relates to a process for the preparation of nitrosobenzene by catalytically reducing nitrobenzene.
A brief summary of processes for the production of nitrosobenzene may be found in U.S. Pat. No. 4,178,315 which is incorporated herein by reference and which specifically discloses a process for the preparation of nitrosobenzene by the catalytic reduction of nitrobenzene utilizing as a reducing agent a compound selected from the group consisting of aliphatic compounds containing from about 1 to about 20 carbon atoms, benzene, naphthalene, and ethylenically unsaturated compounds containing from about 2 to about 10 carbon atoms. In the process of said patent the catalyst which is utilized is preferably a mixture of manganese and lead oxides and the reduction is typically carried out at a temperature in the range from about 250.degree. to about 450.degree. C., in the presence of an inert gas such as carbon dioxide, nitrogen, or a noble gas. In the process the activity and selectivity, as well as the life of the catalyst may be increased substantially by subjecting it to a preliminary treatment with a hydrocarbon or hydrogen. Such a process, in which oxygen-free reducing agents instead of the previously customary oxygen-containing reducing agents, are used for the first time, was found to be superior to the known processes with respect to conversion level, selectivity, and catalyst service life. Therefore, a useful industrial process for the preparation of nitrosobenzene by the reduction of nitrobenzene has been provided through the invention in the aforementioned patent.
An improvement on the process of U.S. Pat. No. 4,178,315 is disclosed in German Pat. No. P 2933314 in which it is shown that in the reduction of nitrobenzene, the addition of small quantities of water to the reaction mixture brings about a considerable increase in conversion. According to such a process, the reduction is carried out in the presence of about 0.05 to about 4 mols of water per mol of nitrobenzene, preferably in the presence of about 0.1 to about 2 mols of water per mol of nitrosobenzene. It was surprising that, under such conditions, in the absence of a reforming catalyst, the addition of water not only accomplishes the reduction with high selectivity just to the stage of the desired nitrosobenzene, but--compared with the process of U.S. Pat. No. 4,178,315--also brings about an increase in reaction rate.
The object of the present invention is to further improve the process which is disclosed in U.S. Pat. No. 4,178,315, and German Pat. No. P2933314.